Most fluorescent lamps in use today are electric discharge lamps, that are usually in the form of a long glass tube coated internally with one or more fluorescent powders, commonly called phosphors. Electrodes are located at each end of the tube that are made with iron, nickel or tungsten, and which are commonly coated with an electron-emissive material. The tube is evacuated and filled at a certain pressure with a noble gas, which is usually argon, neon, krypton or xenon. In addition, there is also inserted in the tube a small drop of mercury which vaporizes during operation of the tube.
In the operation of a fluorescent lamp, an electrical discharge passing from the electrode at one end of the tube to the electrode at the other end, through the noble gas and the mercury vapor, generates ultraviolet radiation. The radiation, in turn, excites the phosphor coating on the wall of the tube to emit visible light.
The phosphors in general use have the characteristic that, when they are excited by ultraviolet radiation of about 253.7 millimicrons wavelength, they will emit visible light. In current designs, the mercury vapor performs the function of converting the energy in an electron discharge into electromagnetic photons of the proper wavelength for exciting the tube phosphor.
The basic lighting mechanism of fluorescent lamp performance is that free electrons emitted from the more negative electrode in the tube collide with the valence electrons of the luminescent gas--in the prior art, mercury vapor. The collision of the discharge electrons with the valence electrons excites the latter by imparting to them part of the kinetic energy of the former, thus raising the valence electrons out of their normal energy level to a level of higher energy. When such an excited electron returns to its equilibrium valence band, part of the excess energy is discarded as surplus, once it returns to its low energy state, is emitted as a lower energy photon.
The predominant measure of efficiency of fluorescent lamp performance is a parameter called "efficacy", which is the ratio of luminous flux output (lumens) to total power input (watts). The highest efficacy theoretically attainable is 680 lumens per watt, which is the output that would be obtained if all the input power were converted to green light at a 555 millimicrons wavelength, the light wavelength to which the human eye is most sensitive. The maximum theoretical efficacy of any light source producing white light with its entire output distributed uniformly with respect to wavelength within the visible region is only 200 lumens per watt. Thus, it can be seen that by concentrating the output wavelength of any light source near the 555 millimicron point, efficacy can be improved beyond that possible with white light. The efficacy of present-day fluorescent lamps is about 55 to 65 lumens per watt.
One of the predominant problems and sources of expense and weight in present-day fluorescent lamps is the necessity for a starting circuit. A fluorescent lamp has a negative resistance characteristics; that is the resistance across the lamp decreases once current begins to flow through the gas in the tube. Moreover, in order to initiate current flow, a much higher voltage must be imposed across the tube than can be used once the tube is operating normally. Thus, present fluorescent lamps must be started by an especially high voltage generated by capacitor storage or some other transient method. Once they have started, they have to operate with some sort of current controls, such as a ballast.
In the course of starting a fluorescent lamp, a high voltage ranging up to 1000 volts may be used to force electron emission from the electrodes into the tube. This type of electron flow will be maintained until the gases in the tube are ionized to sustain the flow with lower voltage. It is the violence of such starting methods on the electrodes and end fittings of the tubes that limits the useful service life of the lamps. In particular, the oxide coating on the electrodes "sputters" during starting, causing the characteristic blackening at the end of the tube and reducing the amount of electron-emissive material on the electrode that is needed to perform the function of providing electron flow in the tube. Not only does the sputtering cut down on the service life of the lamps; it is also the major factor in the lumen maintenance ability of the tube. That is, the capability of the tube to maintain the same output of lumens per watt input throughout its life that it had at some reference time after its service began.
Another disadvantage in present fluorescent lamps is the narrow ambient temperature range in which the lamp can operate. A mercury vapor fluorescent lamp reaches its maximum efficiacy at 77.degree. F., above that point the efficacy falls off about 10 percent for each 20.degree. F. increase, due to the increasing ionization of the mercury vapor molecules, thus precluding ionization due to electron bombardment. As ambient temperature declines from 77.degree. F., the fall-off in efficiency is even more extreme because the mercury droplets present in the tube will not vaporize at all.
Other disadvantages associated with present-day mercury vapor fluorescent lamps include:
the high end losses and inefficiency of the presently used electrodes, PA1 the RFI problem created by the ionization of mercury and its resulting electromagnetic radiation and RFI power line coupling, both of which are capable of creating a buzz in radios that are located in the vicinity of the fluorescent lamp. Although the radiation of RFI can be suppressed somewhat by the use of heavy shielding, the conduction of RFI noise signals back from the electrodes of the fluorescent tube can be prevented only by the use of noise decoupling filters, either in connection with the tube or in connection with the radio sets nearby, and, PA1 since mercury is a known poison and an untold quantity of defective lamps are destroyed and dumped in waste areas. The mercury ends-up as pollution that can poison our water tables. PA1 maintains a constant lumen output over an extended useful operating life, PA1 does not require high start-up currents, PA1 operates over a wide range of ambient temperatures, PA1 is less costly to manufacture due to the elimination of the mercury and the simplified construction of the radiating elements, and PA1 can be manufactured in a variety of geometric shapes.
A search of the prior art did not disclose any patents that read directly on the claims of the instant invention however, the following U.S. Pat. Nos. were considered related:
______________________________________ U.S. PAT. NO. INVENTOR ISSUED ______________________________________ 59-121750 (Japan) Shinto et al 13 July 1984 4,272,703 Eckberg 15 June 1979 3,536,945 Skirvin 27 October 1970 3,189,777 Hoeh 15 June 1965 2,961,565 Lemmers 22 November 1960 ______________________________________
The Shinto patent discloses a cold negative ion electric discharge lamp. The lamp consists of a light permeable outer container which has electric discharge electrodes on both ends and contains mercury and a gaseous body for providing an electric discharge boost. The discharge electrodes consists of a composite metal of lanthanum and nickel or its pulverulent body.
The Eckberg patent discloses a lamp that includes a group of columns positioned within the lamp envelope. Each column has an electron emissive cathode mounted therein connected to a cathode lead-wire. An anode member connected to an anode lead-wire extends to the upper portions of each column. A conductive starter member is mounted within each column to provide a gap between one of its ends and the cathode. A second gap is located between the other of its ends and the associated anode extension. The anode and cathode are energized by a d-c voltage.
The Skirvin patent discloses a luminescent gas tube which includes a mixture of selected gases that operate at resonance which results in a lower power consumption and an enhancement in the luminescence of the tube. There is also disclosed a new type of electrode that has a ball shape with an electron-emission section composed of boroncarbide. The ball electrode produces a high electron emission rate for a given unit of power.
The Hoeh patent discloses a fluorescent lamp that keeps the sputtering of the electrode and the resultant end blackening of the lamp to a minimum. This result is achieved by fabricating the electrodes from a martenistic type stainless steel which is more sputter-resistant than conventional types made from nickel or ferritic stainless steel.
The Lemmers patent discloses a low-pressure discharge lamp wherein the ratio of perimeter to area of the cross section (p/a) is substantially greater than in circular-sectioned lamps of the same perimeter.
By increasing the p/a ratio there is either an improved efficiency at a given wattage per unit length of lamp, or higher wattage loading per unit length for the same efficiency. The ratio increase is achieved by flattening a round tube to an oval or loop-like cross section.